<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <div id="app">
        <h2 class="tittle" :class="['active','line']"> {{message}}</h2>
        <h2 class="tittle" :class="[active,line]"> {{message}}</h2>
        <h2 class="tittle" :class="getClasses()"> {{message}}</h2>
    </div>
    <script src="../js/vue.js"></script>
    <script>
        const app = new Vue({
            el:'#app',
            data:{
                message:'你好呀！',
                active:'aaa',
                line:'bbbbbbbbbb'
            },
            methods:{
                getClasses: function(){
                    return [this.active,this.line]
                }
            }
        })
    </script>
</body>
</html>